Lets try this, could you please log back into your router, which it looks like you know how to do that so I wont explian. Once you are in your router config will you goto WAN SETUP its under advanced. Once you are in there please set NAT FILTERING to OPEN and put a check in DISABLE SIP ALG then hit apply. Reboot the device then restart your xbox.
If this solved your problem please hit ACCEPT on this answer. thanks